Small airways disease: a trial of an easy functional discrimination of preclinical emphysema

In the genesis of small airways obstruction (SAO) we have to consider two alterations with different prognoses: the first, in which the obstruction depends on a reduction of the diameters of the small bronchi (i.e. with prevalent 'intrinsic mechanism)'), is reversible; the second, probably irreversible, is due to pulmonary emphysema in its pre-clinical stage. It is useful to distinguish between these two mechanisms by means of functional tests which are easily applicable in epidemiological screening. We have studied, by means of different lung mechanics tests, 5 normal, male, non-smoking subjects (N) and 10 male smokers considered to be affected by SAO. Several theoretical considerations, experimental data and prospective studies suggest that under various tests of easy execution for a screening program there are some which have, in some cases, a prognostic value and seem to be coupled to a qualitative meaning: this is the case for delta N2 which is significantly greater in subjects of the extrinsic group where the abnormality is considered irreversible. Some other tests are very sensitive to detect SAO subjects by they are lacking in specificity and in prognostic meaning (CV, VEmax, FDC). Finally, other tests [maximal mid-expiratory flow (MMEF) and residual volume (RV)] seem to have a prognostic value only because they indicate an advanced stage of the illness, not depending on the kind of the affection (SAO Ex or SAO In).